1. Field of the Invention
The present invention relates to separation techniques, and particularly to a dispersive liquid-liquid micro extraction (DLLME) method to detect N-nitrosoamines in aqueous solution.
2. Description of the Related Art
N-nitrosoamines (NAs) are produced by the reaction of amines or their derivatives with nitrosating agents, such as nitrous acid, nitrites, or nitrogen oxides. N-nitrosoamines are compounds that are relatively stable and difficult to break down, once formed. NAs have been in the environment, including drinking water, primarily due to the use of ozone in disinfection processes, as well as a variety of other industrial applications, such as food and cosmetics processing, dye and rubber manufacturing, leather tanning and metal casting. NAs have been found in industrial wastewater and in the effluent of sewage treatment plants. NAs are known to have toxic action in the liver, kidneys and lungs of humans. About 90% of NAs are classified as potent human carcinogens, as well as being teratogenic. There are at least four known sources of NAs in water: direct industrial or human-derived contamination; microbial action; disinfection by-product formation; and natural degradation of precursors.
Due to the polarity of NAs, they are typically soluble in water. NAs discovered in drinking water include N-nitrosomorpholine, N-nitrosopyrrolidine, N-nitrosopiperidine and N-nitrosodiphenylamine. The analysis of N-nitroso-di-n-propylamine (NDPA), N-nitrosopiperidine (NPIP) and N-nitroso-di-n-butylamine (NDBA) in water is of particular interest, as these substances have been included in the carcinogenic compounds category B2 included in the Unregulated Contaminant Monitoring Rule 2 of the United States Environmental Protection Agency. Additionally, NAs are known to be rodent carcinogens, and most are considered as probable human carcinogens by the International Agency for Research on Cancer.
Detection of NAs in water typically involves the use of solid phase microextraction (SPME) or liquid-liquid microextraction (LLME) for separation of the compound, followed by ultimate detection and determination performed by gas chromatography (GC) with a variety of detectors, such as a thermal energy analyzer (GC-TEA), nitrogen chemiluminescence detector (NCD), or nitrogen-phosphorus detector (NPD). Mass spectrometry (MS) is often coupled with GC, achieving high sensitivity as well as excellent identification of the analytes. Tandem mass spectrometry (GC-MS/MS) and high resolution mass spectrometry (GC/HRMS) are also often coupled with GC. Liquid chromatography (LC) has also been applied to the determination of NAs in water, using tandem mass spectrometry (LC-MS/MS). However, LC-MS/MS shows relatively low sensitivity for some nitrosamines. SPME is a solvent-free process based on the pre-concentration of analytes from aqueous samples or the headspace of the samples. SPME, however, is a complex and expensive process, primarily due to its use of specialized, fragile fibers with limited lifetimes. Although less expensive, LLME is not seen as an efficient replacement for SPME, as it is a complex, multi-step process that requires a great deal of time to perform.
Dispersive liquid-liquid microextraction (DLLME), however, is a relatively fast extraction technique based on the use of a ternary component solvent system applied to the pre-concentration of both organic and inorganic compounds from aqueous samples. In this technique, a few microliters of a mixture of two solvents (the extractant solvent and the disperser solvent) are quickly injected into the sample. The extractant solvent is immiscible with water, while the disperser solvent is soluble in both water and the extractant solvent. The disperser solvent enables the extractant solvent to disperse and partition into fine droplets uniformly dispersed in the water-disperser solvent matrix, presenting virtually infinite surface area for extraction of the analyte from the aqueous phase into the extraction solvent, which therefore proceeds very quickly, often. This quickly produces a cloudy suspension of fine droplets, which can be centrifuged or simply left to settle in order to separate the extractant solvent (now containing the analyte) from the water-disperser solvent phase. The analyte may then be analyzed by GC or similar methods. It would obviously be desirable to apply the DLLME technique to the determination of NAs, including N-nitroso-di-n-propylamine (NDPA), N-nitroso-di-n-butylamine (NDBA) and N-nitrosopiperidine (NPIP), in aqueous solution.
Thus, a dispersive liquid-liquid microextraction method of detecting N-nitrosoamines solving the aforementioned problems is desired.